The invention relates generally to apparatus and methods for determining fluid levels using ultrasonics. More particularly, the invention relates to ultrasonic fluid level detection without the use of a stillwell.
The use of acoustic transducers for determining fluid levels in containers is well known. In one form of use, an acoustic transducer is mounted within the container so that the transducer emits ultrasonic acoustic pulses directly into the fluid towards the fluid surface. A typical application of this technology is with ultrasonic fuel level sensors for detecting surface levels of fuel in a fuel tank. These sensors typically operate using echo ranging in which an ultrasonic pulse on the order of 1 megahertz is emitted towards the fluid surface. The ultrasonic pulse is reflected at the fuel/air interface and returns towards the sensor in the form of an echo pulse. This echo pulse is then detected by the same or a different sensor. The detection sensor typically produces an output signal that corresponds to receipt of the echo. Thus, the round trip time from pulse emission to echo detection corresponds to the distance of the liquid surface from the sensors.
A typical application of such an intrusive transducer is with fuel tanks used on aircraft. By mounting a transducer at the bottom of a tank, the transducer can be used to emit acoustic pulses towards the fuel surface. The round trip time for the acoustic energy to be reflected back to the transducer can be correlated with the fuel height when the velocity of the acoustic pulses in the fuel is known.
Typically in fuel tank applications, a stillwell is used to reduce the effects of bubbles in the fluid, or fluid swashing around the transducer due to aircraft movement or vibration, as well as to provide a channel for the acoustic waves to follow to the surface of the fluid and back to the sensor. The stillwell also tends to provide a smoother surface for reflecting the acoustic energy.
A stillwell is typically a round or otherwise tubular device that is located in the fuel along the line which measurements are to be taken. The inside diameter is small compared to the size of the tank, such as one inch or less, to reduce wave motion inside the stillwell.
Although the use of stillwells provides benefits such as reducing surface effects, aeration and stratification effects, in some applications it may be desirable not to use a stillwell. Eliminating the stillwell would reduce the amount of in-tank hardware, including eliminating metal or conductive tubes in the tank. Stillwell-less gauging also could increase the attitude range over which readings can be taken, as well as making sensor installation easier, including the possible use of a sensor mounted external the tank.
The objectives exist, therefore, for an acoustic fluid level gauging apparatus and methods that do not use a stillwell inside the fluid container.
To the accomplishment of the foregoing objectives, the invention contemplates, in one embodiment, liquid gauging apparatus for an aircraft fuel tank, comprising: transducer means for emitting acoustic energy into a liquid in the tank in a plurality of predetermined directions towards the liquid surface from a position below the liquid surface and for receiving echoes; and signal conditioning means for determining liquid level based on echo amplitude and time delay between the emissions and detection of the echoes.
The invention further contemplates the methods embodied in the use of such an apparatus, as well as a method for determining liquid level in a container without the use of a stillwell, wherein the container can be subjected to attitude variations, comprising the steps of emitting acoustic energy into the liquid in a plurality of predetermined directions towards the liquid surface from a position below the liquid surface using a plurality of transducers; receiving acoustic echoes using the transducers; and determining liquid level based on echo amplitude and time delay between the emissions and detection of the echoes.